Spray gun, lacquer formulation, and method of directly spraying lacquer

Abstract

The present application provides a kind of spray gun, lacquer formula and the direct spraying method of lacquer, the spray gun is used for spraying lacquer, comprising: gun shell;Spray pot, at the top of the gun shell, the spray pot is used to hold lacquer paint, the end of the spray pot is equipped with miniature stirring device close to the gun shell, the miniature stirring device is used to stir lacquer paint to mix fully;Nozzle, at the front end of the gun shell, the nozzle is communicated with the spray pot;Filtering device is equipped between the spray pot and the nozzle, and the filtering device is used to filter particulate matter in lacquer paint.The present application can realize the direct spraying of lacquer by using spray gun, easy to operate, fills the technical blank that current lacquer process cannot realize spraying process at present, while it is advantageous to improve the quality of lacquer coating.

Description

Technical Field

[0001] This invention relates to the field of lacquer technology, specifically to a spray gun, a lacquer formula, and a direct spraying method for lacquer. Background Technology

[0002] Lacquerware is a great invention of our ancestors, and the lacquer finishing technique is listed as a national intangible cultural heritage. The main material for making lacquerware is "natural lacquer," which is the sap collected from lacquer trees. Currently, the lacquer finishing process generally uses the traditional hand-brushing technique, which has remained almost unchanged for thousands of years. Due to the lack of market competitiveness in terms of quality and mass production, lacquerware has gradually faded from the public eye and is now largely unknown. However, lacquerware possesses unique aesthetic value, once achieving extremely high levels of craftsmanship, and even influencing visual art in the East and the world. Therefore, how to break through the most basic brushing technique in lacquerware finishing has become a bottleneck in revitalizing traditional lacquer culture.

[0003] Existing traditional lacquerware application techniques have many shortcomings, directly leading to low production efficiency, as follows:

[0004] (1) Heavy brush marks: When painting by hand, brushes are used to apply paint, which will produce brush marks during the process;

[0005] (2) Difficult to sand: Manual painting results in uneven paint thickness, many brush marks, and poor flowability. Sanding is required to achieve a smooth surface, which is time-consuming, labor-intensive, and easy to wear through.

[0006] (3) Low efficiency: Manual painting requires extremely high personal skills.

[0007] Larger lacquerware pieces are more prone to problems like heavy brush marks and difficulty in sanding due to the poor flowability of the lacquer. Achieving the desired effect requires a significant investment of labor and time. The high difficulty in producing high-quality lacquerware inevitably leads to lower production efficiency. Current hand-painting techniques make it impossible to mass-produce exquisite lacquerware and maintain consistent quality standards.

[0008] A search revealed a Chinese utility model patent with authorization announcement number CN218132630U, which discloses a special spray gun for artistic paint. The gun uses a stirring rod to continuously agitate the paint inside the spray bottle, ensuring the quality of the paint sprayed from the gun. However, this patent involves stirring during paint mixing, which is insufficient and cannot effectively solve the problem of nozzle clogging during paint spraying.

[0009] Chinese utility model patent CN208261109U discloses a spray gun filter that can effectively filter impurities in the paint, preventing paint particles and impurities from entering the spray gun and damaging it or clogging the oil passages. However, this patent filters the paint before it is poured into the spray bottle, which still fails to solve the problem of nozzle clogging during paint spraying. Summary of the Invention

[0010] In view of the deficiencies in the prior art, the purpose of this invention is to provide a spray gun, a paint formula, and a direct spraying method for paint.

[0011] According to a first aspect of the present invention, a spray gun is provided for spraying varnish, comprising:

[0012] Gun casing;

[0013] A spray bottle, located on top of the gun casing, is used to hold lacquer liquid. A micro-stirring device is provided inside the spray bottle near one end of the gun casing. The micro-stirring device is used to stir the lacquer liquid to ensure thorough mixing.

[0014] A nozzle is located at the front end of the gun housing and is connected to the spray bottle; a filter device is provided between the spray bottle and the nozzle, and the filter device is used to filter particulate matter in the lacquer liquid.

[0015] Optionally, the micro-stirring device includes a stirring blade and a micro motor. The stirring blade is connected to the output end of the micro motor. The size of the stirring blade matches the size of the spray bottle. The stirring blade rotates under the drive of the micro motor, so that the lacquer liquid is fully mixed.

[0016] Optionally, the filtering device has a side-insertion structure, the filtering device includes a filter screen slot and a filter screen, the filter screen slot is a frame structure with an opening, the filter screen slot is provided with insert-type rails on opposite sides, the filter screen has a structure on both sides that matches the insert-type rails, and the filter screen is engaged in the filter screen slot by the rail insertion connection method.

[0017] Optionally, the filter screen has a recessed portion in the middle for accumulating filtered particles.

[0018] According to a second aspect of the present invention, a lacquer formulation suitable for the above-described spray gun is provided, wherein the lacquer formulation comprises, by weight percentage: 70%-80% urushiol, 1%-3% laccase, 3.5%-9% gum, 4%-8% water, and 20%-30% diluent.

[0019] According to a third aspect of the present invention, a method for direct spraying of lacquer is provided, which utilizes the aforementioned spray gun, the method comprising:

[0020] Provide lacquer, mix the lacquer and thinner evenly in a preset ratio, and then put it into the spray bottle of the spray gun;

[0021] Start the micro-stirring device to stir the lacquer liquid;

[0022] Under preset ambient temperature and humidity, paint is applied using a sweeping spray method to form a paint surface on the target workpiece that meets the preset requirements.

[0023] Optionally, the lacquer and thinner are mixed evenly in a preset ratio and then poured into the spray bottle of the spray gun, wherein: the thinner is turpentine or camphor oil; and the ratio of lacquer to thinner is 1:1.35.

[0024] Optionally, the preset ambient temperature and humidity include: a temperature of 20-35℃ and a relative humidity of 70-80%.

[0025] Optionally, the paint is applied by sweeping and spraying, wherein the spraying air pressure is 0.3-0.6 MPa.

[0026] Optionally, the paint is sprayed using a sweeping spray method, wherein the spraying distance is determined according to the spraying concentration and spraying air pressure, and the paint sprayed from the spray gun meets the adhesion requirements of not flowing or rebounding on the surface of the target workpiece.

[0027] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0028] 1. This invention, by incorporating a micro-stirring device and a filtering device inside the spray gun, ensures more thorough mixing of the paint liquid, reduces the frequency of nozzle clogging, and enables direct spraying of lacquer using the spray gun. It is easy to operate, requires little technical expertise from the user, greatly improves efficiency, and solves the technical problem of nozzle clogging when spraying lacquer.

[0029] 2. This invention can form a smooth and dense lacquer coating after direct spraying, without brush marks, with uniform coating thickness and a very smooth surface. It can improve the efficiency of lacquerware production and improve the quality of the lacquer coating. It solves the problems of low efficiency and inability to achieve mass production in traditional manual lacquer painting techniques, and fills the technical gap in the current lacquer process that cannot achieve spraying. Attached Figure Description

[0030] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0031] Figure 1 This is a schematic diagram of the spray gun structure in one embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of the filter screen in one embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the filter screen slot in one embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the structure of a micro motor in one embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram of direct lacquer spraying in one embodiment of the present invention.

[0036] In the diagram: 1 is the nozzle, 2 is the spray bottle, 3 is the stirring blade, 4 is the micro motor, 5 is the battery, 6 is the filter slot, and 7 is the filter. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0038] In existing technologies, the spray gun, as a major component of spraying equipment, consists of a gun body, spray bottle, and nozzle, and is mainly used for spraying chemical paints. Lacquer, the sap extracted from lacquer trees, is purely natural and belongs to the category of natural (biological) coatings. When lacquer is mixed with natural mineral pigments, it cannot achieve the same level of integration as chemical paints. Because the lacquer contains a large number of mineral particles, using existing spray guns will cause nozzle clogging, preventing successful spraying. To solve the problem of spray gun nozzle clogging when spraying lacquer, [the following is a proposed solution]... Figure 1-4 An embodiment of the present invention provides a spray gun for spraying lacquer, comprising a gun housing, a spray bottle 2, and a nozzle 1 (i.e., a spray head). The spray bottle 2 is located at the top of the gun housing and is used to hold the lacquer liquid. A micro-stirring device is provided inside the spray bottle 2 near one end of the gun housing to stir the lacquer liquid for thorough mixing. The nozzle 1 is located at the front end of the gun housing and is connected to the spray bottle 2. A filtering device is provided between the spray bottle 2 and the nozzle 1 to filter particulate matter in the lacquer liquid. This embodiment of the present invention provides a micro-stirring device inside the spray bottle 2 to ensure more thorough mixing of the lacquer liquid during spraying; the filtering device provides finer lacquer filtration before the stirred lacquer liquid enters the nozzle 1, thereby minimizing the risk of nozzle 1 clogging.

[0039] In some embodiments, the micro-stirring device includes a stirring blade 3 and a micro motor 4. The size of the stirring blade 3 matches the size of the spray bottle 2. The stirring blade 3 is connected to the output end of the micro motor 4. The micro motor 4 is powered by a battery 5. Preferably, the battery 5 is a button battery. The button battery is installed on one side of the micro motor 4. A start switch is provided on the outside of the micro motor 4. The stirring blade 3 rotates under the drive of the micro motor 4, so that the lacquer liquid is fully mixed.

[0040] In some embodiments, the filter device has a side-insertion structure, including a filter screen slot 6 and a filter screen 7. The filter screen slot 6 is a frame-shaped structure with an opening, and the filter screen 7 is housed within the opening, forming a square filter device for easy installation and miniaturization. The filter screen slot 6 has insertion rails on opposite sides, and the filter screen 7 has structures on both sides that match these insertion rails. The two are connected by a rail insertion method, allowing the filter screen 7 to engage within the filter screen slot 6. The filter screen 7 can be easily moved by inserting and removing it. During spraying, the filter screen 7 is removed and replaced according to the amount of impurities on the filter screen. The spray bottle 2 and the nozzle 1 are connected by a spray gun tube. The diameter of the filter screen 7 is the same as the diameter of the circular spray gun tube at the lower outlet of the spray bottle 2, effectively reducing the frequency of nozzle clogging.

[0041] It should be noted that, in addition to the square structure described above, the filter device can also adopt other structures such as rectangles, and the embodiments of the present invention do not specifically limit this.

[0042] In some embodiments, the filter screen 7 has a recess in the middle for accumulating filtered particles, preventing particles from entering the nozzle 1 and minimizing the probability of nozzle 1 clogging.

[0043] In the above embodiment, a micro-stirring device is installed inside the spray bottle 2 connected to the upper end of the spray gun. When the paint enters the spray gun tube through the spray bottle 2, the micro-stirring device is activated, causing the stirring blades 3 inside the upper spray bottle 2 to rotate, thus stirring the paint. The stirred paint is more thoroughly mixed, reducing the frequency of nozzle clogging. A filter device is installed at the upper end of the connection between the spray bottle 2 and the spray gun tube. This device is a left-right side-insertion type with a track for inserting and removing the filter screen 7. The filter screen 7 has a recessed center that stores a certain amount of particulate matter, facilitating filter screen 7 replacement and minimizing the probability of nozzle 1 clogging. This allows for direct spraying of paint using the spray gun, which is simple to operate, requires little technical skill from the user, and greatly improves efficiency.

[0044] Another embodiment of the present invention provides a lacquer formula suitable for the above-mentioned spray gun. By weight percentage, the lacquer formula includes: 70%-80% urushiol, 1%-3% laccase, 3.5%-9% gum, 4%-8% water and 20%-30% diluent.

[0045] Urushiol is the main film-forming substance and is insoluble in water. The higher the urushiol content, the better the quality of the lacquer. Lacquer drying occurs through the oxidation of urushiol in the lacquer, causing it to oxidize and polymerize in the air, thus forming a film. The oxidizing substance in lacquer is laccase, an oxidase essential for the natural drying of lacquer. As a drying agent for lacquer, laccase activity is greatly affected by ambient temperature and humidity. Specifically, laccase exhibits significant heat sensitivity. Its activity is highest and the lacquer dries fastest when the temperature is 20-35℃ and the relative humidity is 70-80%, preferably at 30℃ and 80%. However, at 75℃, laccase activity is completely destroyed within one hour. Applying lacquer in excessively hot or cold weather, or in excessively dry or humid environments, will hinder drying.

[0046] Gum is a film-forming binder, and its presence and content have a significant impact on the viscosity and quality of lacquer. It enables the main components of lacquer to form a uniformly distributed emulsion and stabilizes it, preventing it from easily deteriorating. Moisture is naturally present in lacquer; lacquer with less than 4% moisture is extremely difficult to air dry. Thinners are used to dilute the lacquer liquid; natural turpentine, natural camphor oil, and natural orange oil are suitable thinners.

[0047] Through the synergistic effect between the various components and their contents in the lacquer, the lacquer in the above embodiments has properties such as hard film formation, fast drying, good leveling properties, and bright gloss. The lacquer formula meets the basic parameters for spray gun spraying (including lacquer spraying concentration, air pressure, spraying distance, etc.), thereby enabling direct spraying of lacquer using a spray gun.

[0048] Another embodiment of the present invention also provides a method for direct spraying of lacquer, which is implemented using the spray gun described above, and continues to refer to... Figures 1-4 and combined Figure 5 The method includes:

[0049] S1. Provide lacquer, which adopts the lacquer formula in the above embodiment. Mix the lacquer and thinner evenly in a preset ratio and then put them into the spray bottle of the spray gun.

[0050] S2. Start the micro-stirring device to stir the lacquer liquid.

[0051] S3. Under the preset ambient temperature and humidity, apply the paint using a sweeping spray method to form a paint surface on the target workpiece that meets the preset requirements.

[0052] The main considerations for lacquer spraying are the thinner, dilution ratio, and the degree of impurity filtration. Lacquer needs to be diluted before spraying. Common thinners for lacquer include turpentine, camphor oil, tung oil, gasoline, and thinner. Thinner, also known as banana oil, has a strong banana odor and is highly compatible and stable with lacquer. However, thinner is a volatile and harmful substance that can enter the human body through the skin and respiratory tract. Gasoline has an anesthetic effect on the central nervous system; long-term inhalation of excessive amounts can cause serious harm. If these materials are added to lacquer for dilution, many harmful substances will be incorporated, compromising the lacquer's natural purity. Therefore, it is not recommended to use thinner or gasoline as lacquer thinners. Adding too much tung oil as a thinner will affect the drying of the lacquer and soften the lacquer film. Therefore, turpentine or camphor oil is preferred as a thinner. The thicker the lacquer, the more difficult it is to spray, the harder it is to spray evenly, and the harder it is to dry. Even after drying, the lacquer surface is prone to wrinkling. Furthermore, the thicker the lacquer, the higher the required air pressure, making it more prone to rebound and clogging the spray gun. Therefore, the lacquer concentration should be relatively thin rather than thick. Preferably, the ratio of lacquer to thinner is 1:1.35. Using this dilution ratio, the lacquer, after being diluted and placed in the spray bottle, will not stick to the bottle wall, facilitating subsequent spraying operations. Filtering impurities during lacquer spraying is achieved through the spray gun's filtration device, thereby obtaining a dense and smooth lacquer coating.

[0053] It should be noted that lacquer will separate into layers if stored for a long time. Diluting it without thorough stirring will result in inaccurate dilution ratios. Therefore, the lacquer must be stirred thoroughly before mixing. Additionally, in practice, black lacquer and clear lacquer can be diluted more concentratedly, while colored lacquer can be diluted more thinly. When diluting colored lacquer, the saturation and gloss of the color must also be considered.

[0054] A clean and temperature- and humidity-controlled environment is crucial for lacquer spraying. In some implementations, the preset ambient temperature and humidity include: a temperature of 20-35°C and a relative humidity of 70%-80%. During lacquer spraying, the spraying workshop should closely approximate the drying characteristics of the lacquer. To accommodate the drying characteristics of the lacquer, a dedicated room (or basement) is needed as a drying chamber for drying the lacquer coating. The chamber should be clean, dust-free, and unventilated; preferably, the room temperature should be controlled at 25°C. The floor and walls should be regularly moistened to maintain a relative humidity of approximately 80%. This temperature is within the range where laccase activity is maintained, allowing the lacquer to dry rapidly in the air to form a film, while also ensuring the comfort of the workers.

[0055] In the above embodiments, using a sweeping spray method avoids the unevenness of the object surface caused by excessive lacquer buildup in one position on the spray gun. The spraying air pressure refers to the value after pressing the trigger. Lacquer sprayed out is glossy; a thick coat will result in a matte finish and wrinkling. Excessive spraying air pressure causes the lacquer to bounce off the workpiece surface, forming noticeable lacquer mist. This mist adheres to the lacquer surface and, after drying, becomes rough like sandpaper. Furthermore, higher spraying air pressure results in greater impact on the workpiece surface, necessitating long-distance spraying. If the spraying distance is too far, the lacquer on the workpiece may be blown away. In some embodiments, a sweeping spray method is used for lacquer spraying, where the spraying air pressure is 0.3-0.6 MPa. This air pressure prevents the lacquer from bouncing off the workpiece surface and avoids excessive impact, thus promoting a smooth lacquer coating.

[0056] After being sprayed from the spray gun, the paint forms a triangular pyramidal coverage pattern. The farther the spraying distance, the larger the coverage area, the thinner the paint layer upon reaching the workpiece, and the less impact force the air pressure exerts on the workpiece surface. Spraying too close will create paint mist, while a close distance with high paint concentration will cause the paint to granulate before reaching the surface. The spraying distance is determined by the paint concentration and spraying air pressure. Furthermore, the paint output needs to be adjusted during spraying. A higher output results in better coverage but also makes it easier for paint to accumulate. For example, in flat spraying operations with a single coverage area not exceeding 40cm in diameter, under conditions of a 1:1.35 dilution ratio and 1.5 atmospheres of pressure, the spraying distance is approximately 15cm, and the paint output is used to measure coverage, ensuring the paint reaches the workpiece surface without dripping. It should be noted that if the single coverage area is larger or smaller, the parameter combinations need to be adjusted to achieve a paint that does not drip or bounce upon reaching the workpiece surface.

[0057] The effect and feel of lacquer spraying are related to the type of lacquer, its concentration, air pressure, paint output, and spraying distance. If the lacquer is too thin, the distance is too short, the air pressure is too high, or too much is sprayed, it will cause dripping and poor adhesion. If the lacquer is too thick, the distance is too far, or the air pressure is too low, the lacquer will be too thin and float on the workpiece surface, causing the lacquer to bounce back. The effect achieved by lacquer spraying is the result of the combined effect of multiple spraying parameters, not determined by a single factor. The lacquer spraying method in the above embodiments can meet the requirements of speed, humidity, and dilution of the lacquer when it is sprayed from the spray gun and travels a certain distance to adhere to the workpiece surface, achieving a near-semi-dry adhesion state. That is, the lacquer sprayed from the spray gun meets the adhesion requirements of not dripping and not bouncing on the target workpiece surface, thereby forming a smooth, dense, uniformly thick, and smooth lacquer coating.

[0058] The comparison between the direct spraying method of lacquer in the above embodiments and the manual painting process in the prior art is shown in Table 1 below.

[0059] Table 1. Comparison of direct spraying and manual brushing methods for lacquer.

[0060] project Existing manual painting process direct paint spraying process brush marks have none Polishing Difficult to penetrate, easy to break through easy advection Difference good Mass production Unable to achieve mass production Mass production is possible Quality control Quality control is difficult to achieve with individual skills. Standardized operating parameters enable quality control. standardization Unable to achieve standardization Standardizable

[0061] The above embodiments of the present invention, by setting a micro-stirring device and a filtering device inside the spray gun, enable more thorough mixing of the paint liquid, reduce the frequency of nozzle clogging, and realize direct spraying of paint using the spray gun. The operation is simple, does not require high technical skills from the user, greatly improves efficiency, and solves the technical problem of nozzle clogging when spraying paint.

[0062] In the above embodiments of the present invention, considering that lacquer, as a plant-based paint, does not blend as thoroughly as chemical paints, a micro-stirring device is used to stir the lacquer after mixing and stirring. This allows for secondary synchronous stirring during spraying from the spray bottle, ensuring more thorough mixing of the lacquer liquid. After the paint liquid is poured into the spray bottle and undergoes secondary stirring by the micro-stirring device within the bottle, it undergoes secondary filtration using a filter device before entering the spray gun. The filter screen can be replaced at any time during the spraying process based on the amount of impurities, fundamentally and thoroughly removing impurities. This approach is flexible and practical. Therefore, it effectively solves the problem of nozzle clogging during lacquer spraying, thus enabling a lacquer spray gun application process.

[0063] The above-described embodiments of the present invention can form a very smooth and dense lacquer coating after direct spraying, without brush marks, with uniform coating thickness and a very smooth surface. This can improve the efficiency of lacquerware production and improve the quality of the lacquer coating. It solves the problems of low efficiency and inability to achieve mass production in traditional manual lacquer painting techniques, and fills the technological gap in the current lacquer process that cannot achieve spraying.

[0064] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A method for direct spraying of lacquer, characterized in that, This can be achieved using a spray gun, including: Provide lacquer, mix the lacquer and thinner evenly in a preset ratio, and then put it into the spray bottle of the spray gun; Start the micro-stirring device to stir the lacquer liquid; Under the preset ambient temperature and humidity, the paint is sprayed using a sweeping spray method. During the spraying process, the paint is simultaneously stirred in the spray bottle to form a paint surface that meets the preset requirements on the target workpiece. The spray gun is used for spraying paint, including: Gun casing; A spray bottle, located on top of the gun casing, is used to hold lacquer liquid. A micro-stirring device is provided inside the spray bottle near one end of the gun casing. The micro-stirring device is used to stir the lacquer liquid to ensure thorough mixing. A nozzle is located at the front end of the gun housing; a filter device is provided between the spray bottle and the nozzle, the filter device being used to filter particulate matter in the lacquer liquid; The micro-stirring device includes a stirring blade and a micro motor. The stirring blade is connected to the output end of the micro motor. The size of the stirring blade matches the size of the spray bottle. The stirring blade rotates under the drive of the micro motor, so that the lacquer liquid is fully mixed. The filtering device includes a filter screen slot and a filter screen, wherein the filter screen is engaged in the filter screen slot via a track insertion connection. The spray bottle and the nozzle are connected by a spray gun tube, and the diameter of the filter screen is the same as the diameter of the circular spray gun tube at the lower outlet of the spray bottle; The lacquer formulation suitable for the spray gun comprises, by weight percentage: 70%-80% urushiol, 1%-3% laccase, 3.5%-9% gum, 4%-8% water, and 20%-30% diluent.

2. The direct spraying method for lacquer according to claim 1, characterized in that, The lacquer and thinner are mixed evenly in a preset ratio and then poured into the spray bottle of the spray gun, wherein: the thinner is turpentine or camphor oil; the ratio of lacquer to thinner is 1:1.

35.

3. The direct spraying method for lacquer according to claim 1, characterized in that, The preset ambient temperature and humidity include: a temperature of 20-35℃ and a relative humidity of 70-80%.

4. The direct spraying method for lacquer according to claim 1, characterized in that, The paint is applied using a sweeping spray method, wherein the spraying air pressure is 0.3-0.6 MPa.

5. The direct spraying method for lacquer according to claim 1, characterized in that, The method of spraying paint is described, wherein the spraying distance is determined according to the spraying concentration and spraying air pressure, and the paint sprayed from the spray gun meets the adhesion requirements of not flowing and not rebounding on the surface of the target workpiece.

6. The direct spraying method for lacquer according to claim 1, characterized in that, The filter device has a side-insertion structure, the filter screen slot is a frame-shaped structure with an opening, the filter screen slot has insertion rails on opposite sides, and the two sides of the filter screen have a structure that matches the insertion rails.

7. The direct spraying method for lacquer according to claim 1, characterized in that, The filter screen has a recessed portion in the middle, which is used to collect filtered particles.

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